Telephone system



Aug. 28, 1934. sMlTH 1,971,509

TELEPHONE SYSTEM Filed Dec. 11. 1931 [W Howard H. ErfiH-L Patented Aug. 28, 1934 UNITED STATES TELEPHONE SYSTEM Howard H. Smith, Chicago, Ill., assignor to Assooiated Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application December 11, 1931, Serial No. 580,273

4 Claims.

The present invention relates in general to telephone systems. The main object of the invention is to reducethe ill eiiects resulting from arcing at the interrupter or impulsing contacts.

In spite of numerous precautions which may be taken to'prevent arcing at contacts which are used to interrupt inductive circuits at relatively high rates, there is always some arcing present between such contacts. The are which isfformed between the contacts at each interruption tends to eat away one of the contacts and deposit the metal on the other contact, that is, the contact metal is carried from one contact to the other. When the current flow through the contacts is always. in the same direction, the result is that one of the contacts is gradually eaten away and the other built up, thereby causing the. interrupter or impulsing relay to become out of adjustment.

It has been proposed to reverse the battery connections to contacts of this type by means of a manually operated switch to reduce this transfer of metalirom one contact to theother. However, this is objectionable .in that the switch must be manually operated at frequent intervals, thereby requiring nearly constant attention. Also, when the switch is manuallyoperated at definite intervals there is no assurance that the carrying over of the contact metal will be the same in each direction, since the contacts may be used very little when the current is in one direction while they may *be in continuous use whenthe current is in the other direction. Furthermore, the reversals should be made at frequent intervals which is impractical if they are to be made by means of a manually operated switch. 1 r

A particular feature of the present invention, therefore, is the provision ofmeans for automatically reversing the battery connections to impulsing or interrupter contacts at intervals which will insure approximately equal operations of the contacts. during each reversal of the currentsupply.

The objects and featuresof the invention may best be understood from a perusal of the following specification when read in connection with the accompanying drawing, comprising one figure only, which shows bymeans of the usual schematic diagram jsuficient of the. apparatus in a telephone system to, enable the invention to be understood. v i

Referring to the drawing, the invention has been shown as. applied to a telephone system in which alternating currents of .voice frequency winding of this transformer, the circuit of which are used for dialling and signalling. A system of this type is fully disclosed in a co-pending joint application of Smith and Wicks, serial No. 550,436, filed ,July 13, 1931 now Patent No. 1,932,235, granted Oct. 24, 1933. The toll selector T81 indicated by the rectangle in the upper left-hand portion of the drawing may be identical with the toll selector T51 shown in Fig. 1 of the above-mentioned application. The voice frequency repeater R1 indicated by the rectangle in the lower left-hand portion of the drawing may be identical with the repeater R1 disclosedin Fig. 2 of the above-mentioned application. -The tone group TGl indicated in skeleton form in the upper portion of the drawing is similar to the tone group 'I'Gl disclosed in the upper portion of Fig. 3 of the drawing in the above-mentioned application, being slightly modified by the addition of the reversing arrangement of the present invention. The reference characters applied to the various elements of the drawing which also appear in the above-mentioned application of Smith and Wicks are identical with the reference characters used in that application.

A detailed explanation of the operation of the invention will now be given. The trunk line comprising conductors 20 and 21 extends to a distant exchange and terminates in a tone group, I a toll selector, and a voice frequency repeater similar to tone group TGl, toll selector TSl, and repeater R1, respectively. When signals of voice frequency alternating current such as'the seizing signal, dialling impulses, and supervisory signals are received from the distant exchange over trunk line conductors 20 and 21, relayasoo is in its normal position and these alternating currents pass through the condenser 325 and the primary winding of transformer 326. Corresponding currents are induced in the secondary winding of the transformer and impressed on the grid of the amplifying tube 310. The resulting plate current through the primary winding of transformer 319 is induced in the secondary includes the voice frequency tuned relay 322 which is tuned to respond to the frequency used forsignalling. This frequency may, for example, I

be of theorder of 1000 cycles per second.

The voice frequency tuned relay 3 22 responds to L signals of 1000 cycles per second, and the tuned reed armature 323, which is tuned to respond to this frequency, vibrates, each time a signal is received. By operating the spring 324 it opens the impulsing and signalling circuit extending to the voice frequency repeater R1 and toll selector T51 over conductor Z. The signals consist of thousand-cycle alternating current interrupted at various rates such as thirty, forty two, fifty four, and sixty six times per second. The thousand-cycle current is interrupted ten times per second to transmit the dialling impulses.

Each time an impulse of thousand-cycle current is received, the relay 322 responds and opens its impulsing contacts to repeat the impulse to the voice frequency repeater R1. Thus it is seen that during the establishment of the call the impulsing contacts 324 of the voice fre quency relay 322 are interrupted at varying rates from ten interruptions to as high as sixty six interruptions per second. If the current through these contacts were always in the same direction, the contact metal on one spring would be gradually carried away and deposited on the other spring, thereby causing the relay to become out of adjustment and necessitating frequent replacement of the contact springs. In order to prevent this, the reversing arrangement comprising relays 101'and 102 and various contacts has been provided.

When the trunk line comprising conductors 20 and 21 is first seized for an incoming call, a seizing signal is transmited thereover and received by the voice frequency relay 322 which in turn repeats the signal to the voice frequency repeater R1, thereby preparing the toll selector TSl for operation. As soon as the toll selector TSl is seized, ground is placed on the busy conductor by the voice frequency repeater R1. This operation is explained in detail the above-mentioned joint application of Smith and Wicks. This ground extends over conductor 2 to the toll selector T81 and over conductor 10 to the banks of selectors having access to the inter-office trunk line. This ground is also extended over conductor 100, armature 104 and its resting contact, lower winding of differential relay 101, to battery. ihe ground also extends through the normally closed springs controlled by armature 103 to the upper terminal of the winding of relay 102, but this winding is shunted by ground connected to its lower terminal through armature 104 and its resting contact.

Relay 101 operates over its lower winding and at armature 103 and its working contact connects direct ground to the upper terminal of the winding of relay 102. However, this relay is shunted as long as the busy conductor 100 is grounded. Thus, throughout the call, ground is connected to the right-hand spring of the impulsing contacts 324 through the normally closed springs controlled by armature 106, and the impulsing conductor Z extending to the voice frequency repeater R1 is connected to the lefthand spring of the impulsing contacts through the normally closed springs controlled by armature 105.

At the termination of the call, ground is removed from the busy conductor 100 after the toll selector T81 and repeater R1 have restored to normal, thereby removing the shunting ground from the lower terminal of the winding of relay 102. This relay now operates iii-series with the lower winding of relay 101 from ground, armature 103 and its working contact, winding of relay 102, lower winding of relay101, to battery. At armature 104 and its resting contact it opens its shunting circuit and at the working contact of this armature it prepares a circuit for the upper winding of relay 101. At armature 105 it disconnects the impulsing conductor Z from the left-hand s ring of the impulsing contacts 324 and connects direct ground. to this spring. At armature 106 it disconnects ground from the right-hand spring of the impulsing contacts and connects this spring to the impulsing conductor Z. The battery connections to the impulsing contacts have now been reversed, that is, current through the impulsing contacts is now in the opposite direction.

When the trunk line comprising conductors 20 and 21 is seized for the next call, busy conductor 100 is grounded by the voice frequency repeater R1, either on an incoming or an outgoing call, thereby completing a circuit for the upper winding of relay 101 from ground on conductor 100, armature 104 and its working contact, upper winding of relay 101, to battery. The two Windings of relay 101 are differentially wound so that when both of its windings are energized the relay releases. At armature 103, and its working contact it opens the locking circuit for relay 102 and at the normally closed springs controlled by this armature it substitutes the ground which is present on conductor 100 to maintain relay 102 energized. As long as conductor 100 remains grounded, relay 102 is held energized in series with the lower winding of relay 101. The 'wo windings of relay 101 are both energized and, being diiferentially wound, this relay remains deenergized. Thus, during this call, relay 102 is held energized and maintains the battery connections to the impulsing contacts 324 reversed. Thus the current through these impulsing contacts is in the opposite direction to what it was during the previous call and any transfer of contact metal which took place during the previous call is now compensated for by the transfer in the opposite direction.

At the end of this call, ground is again removed from conductor 100, thereby removing ground from the upper terminal of the winding of relay 102 and also from the upper winding of relay 101. Relay 102 accordingly deenergizes and relay 101 remains deenergized. When relay 102 deenergizes it again reverses the connections to the impulsing contacts 324 at armaturcs 105 and 106, and at armature 104 and its resting contact it again prepares the initial energizing circuit for relay 101.

From the foregoing description, it is seen that the connections to the impulsing contacts 324 are reversed after each call, thereby insuring that approximately the same number of operations of the impulsing contacts take place with the current in one direction as with the current in the other direction. By this arrangement, the continual building up of one contact and corresponding eating away of the other contact is prevented and the transfer of metal taking place during one call is compemated for by the reverse transfer during the succeeding call. In this way, the relay is kept in adjustment and requires very little attention.

Although the invention has been shown and described as applied to impulsing contacts in a voice frequency dialling telephone system, it is to be understood that the invention is not limited to this application but is equally applicable to various other interrupter and impulsing contacts which are used to interrupt inductive circuits at relatively high rates. Thus, it might be applied to the vibrating contacts on vibrating type ringing machines and to various tone buzzers and interrupter circuits.

What is claimed is:

1. In a telephone system, a circuit, a pair of interrupter contacts and a battery included in said circuit, means for operating said contacts intermittently during the establishment of telephone connections, means for reversing the connections to said pair of contacts, and means depending on the frequency of establishment of connections for controlling said reversing means.

2. In a telephone system, a trunk, means for establishing telephone connections over said trunk, a relay intermittently operated over said trunk to assist in the establishment of connections, a control circuit including contacts on said relay and a source of current, and means for reversing the connections to said contacts each time a connection established over said trunk is released to prevent excessive transfer of contact metal between said contacts due to arcing when the contacts are opened.

3. In a telephone system, a trunk including a busy conductor to which ground potential is applied when the trunk is seized and removed when the trunk is released, a. pair of contacts intermittently operated during the establishment of telephone connections over said trunk, a circuit including said pair of contacts and a source of current, and means effective each time ground potential is removed from said busy conductorfor reversing the connections to said pair of contacts.

4. In a telephone system, a trunk circuit including an impulsing relay, a busy conductor to which ground potential is applied each time the trunk is seized and removed each time the trunk is released, an impulsing circuit including a source of current and a pair of contacts on said relay, a second and a third relay, means for changing the operated or unoperated condition of said second relay each time ground potential is applied to said busy conductor and of said third relay each time ground potential is removed from said conductor, and contacts on said third relay for reversing the connections to said pair of contacts.

HOWARD H. SMITH. 

